There are traditionally two different types of piston rings, oil control rings and compression rings. Typically, the piston assembly includes one or more compression rings to generate a seal between the outer surface of the piston and an inner surface of the liner of the combustion chamber. An inner end of the compression ring fits into a tapered groove on the outer surface of the piston while an outer wall of the ring makes contact with the inner surface of the liner. The outer wall of the compression ring generates the seal in the space between the piston and the liner to prevent high-pressure combustion gases and air from escaping.
Typical prior art piston assemblies are shown in FIGS. 1a and 1b. The assembly 10 includes a piston 12 and a piston ring 14. The seal formed by the piston ring 14 prevents combustion gases and air from escaping the combustion chamber with each stroke of the piston 12. The piston ring 14 includes an inner peripheral wall 20, an outer peripheral wall 22, a first side wall 24 and a second side wall 26. The first side wall 24 and the second side wall 26 extend from the inner peripheral wall 20 to the outer peripheral wall 22. As shown, the prior art piston rings 14 have angles, A, generated by the outward convergence of the side walls 24, 26. In the prior art, the angles, A, are equal, for example, each angle, A, would be approximately 7.5 degrees.
To improve the seal of the ring 14, manufacturers have found it desirable to twist the ring 14 within a tapered groove 30 of a piston 12. Twisting the ring 14 causes an edge 28 of the outer peripheral wall 22 of the ring 14 to bear against a liner (not shown) with an increased force as compared to the rest of the outer peripheral wall 22. This increased force on the edge 28 of the outer peripheral wall 22 generates a more effective seal and prevents leakage of gases, air and lubricating-oils between the liner and the outer peripheral wall 22. Furthermore, twisting the ring 14 within the groove 30 reduces the clearance between the ring 14 and the groove 30 to provide continuity of the seal. To twist the ring 14, traditionally the first side wall 24 is beveled to generate an intermediate wall, B. The intermediate wall, B permits the ring 14 to twist within the tapered piston groove 30 and provide a better seal when contacting the liner and the piston 12.
To manufacture the conventional piston ring 14 with the beveled intermediate wall, B, and the resultant twist feature, the piston ring 14 is first machined to generate the two side walls 24, 26 at equal angles, A. Typically to produce the beveled intermediate wall, B, an additional machining process is necessary to remove the material from the first side wall 24. This additional machining process is time consuming. Alternatively, other techniques for generating the beveled intermediate wall, such as making the ring 14 from near net shape wire to include the beveled intermediate wall, B, are commonly used in the industry.